We have continued, during this fiscal year, our investigation into the nature of the rapid structural changes in the nervous tissues associated with the process of excitation. Last year, we found, employing the electric organ of the ray known for its massive cholinergic innervation, that the chemical transmitter released from the nerve endings evokes rapid swelling (a rise in the water content) in the postsynaptic elements. We have demonstrated, during the early period of this fiscal year, that these mechanical changes are accompanied by large, readily detectable optical changes in the tissues, i.e., by a pronounced fall followed by a sustained rise in light scattering. We believe that the release of Ca-ions from the postsynaptic membrane triggered by the chemical transmitter release (Neuman et al., 1973-1976) is at the base of these mechanical and optical changes. Later on, we devoted our effort to the development of a new type of heat detector by using extremely thin polyurea film (Takahashi et al., J. Appl. Phys. 70;6983, 1991). By virtue of the large dipole moment carried by the urea groups in the polymer, it was found possible to endow such film with strong pyroelectricity. Responding to our request, Tsukuba Institute for Super Materials in Japan sent us samples of pyroelectric polyurea film (deposited on five-micron thick mylar layer). The records of thermal changes in the ray electric organ, obtained with the detectors we have fabricated recently, appear to indicate that the onset of heat production by the tissue is roughly simultaneous (within 0.5 msec) with the osnet of the postsynaptic potential.